The cutoff value to estimate the resolution value can be defined by:
- the point of the curve where the correlation is 0.5
- the point of the curve that crosses a significance threshold curve
According to Orlova et al. 1997 (J Mol Biol, 271:417) this significance
threshold curve is defined as the 3*sigma (sigma = standard deviation of
the FSC) for non-symmetrical particles. (units: 1/A)
[stc stands for significance threshold curve]